This can occur for different reasons:
When there are two separate instances of TaskCentre running.
To resolve this issue:
Disable the server service on the instance that is a duplicate by logging on to the server hosting the software.
Run the services snap-in.
Right-click on the TaskCentre Server Service.
Select Properties.
Change the Startup Type to Disabled.
When there are two MSSQL trigger agents configured.
To resolve this issue:
In the case that there are two agents configured, unregister one of the agents by logging in to TaskCentre.
Expand the System node.
Click on Agents.
Right-click on the agent to unregister.
Select Unregister.